Electrical conductors may for example be used in power transmission and distribution applications, and in power transformation. In these applications it is desirable to electrically insulate electrical conductors such that they do not short-circuit and thereby damage electrical equipment and/or cause injury to people.
GB 943 151 discloses an example of a method of insulating electric cables and conductors with an insulating plastic material. The conductor is drawn through a bath of molten plastic material and thereafter through a die. The die has a conical hole, and the cone angle is 6-12 degrees, and the smallest diameter of the conical hole is 20-30% larger than that of the uncoated conductor.
U.S. Pat. No. 4,521,173 discloses an apparatus for the manufacture of a coated filament such as a magnet wire. The method may comprise heating the filament, depending on the coating material utilized and the wire properties desired. In this case, the filament is heated by means of a heating device to a temperature of about decomposition temperature. In most applications the filament is heated to about the melting point of the coating material. The filament then travels through a die where the coating is applied.
For high voltage and medium voltage applications it is especially important that the electrical insulation provided around a conductor is reliable, as for example, the electrical insulation may progressively be destroyed due to repeated corona/partial discharges generated within the insulated electrical conductor.
The electrical insulation of many existing electrically insulated electrical conductors is hence prone to progressive destruction.